The present invention relates to a coating composition capable of giving a surface coating having improved surface properties. Generally, coating films formed by application of a conventional coating material have disadvantages such as damage and stain or dullness of the surface when coming into contact with other bodies. The undesirable tendency is particularly prominent when the coating film formed of the coating material has relatively low mechanical strength.
That is, finished plywood boards prepared by coating with a nitrocellulose lacquer, an aminoalkyd resin coating or a polyurethane coating and steel sheets coated with an acrylate coating or so-called precoated steel sheets and the like, for example, have shortcomings including sticking together and damage or appearance of dullness of film surfaces when they are placed in a stack or as rolled in a coil and, furthermore, breaking of coating films when a pressure-sensitive adhesive tape is applied and then peeled off due to partial transfer of the coating film to the adhesive tape, Moreover, such coating-finished plywoods have another disadvantage of a so-called blocking phenomenon during processing of them using an adhesive at the time of removal of the contaminating adhesive from the coated surface because the coating film is also removed as being carried by the adhesive.
In consideration of the above, there have been made several proposals with an object of removing such disadvantages including a coating composition by admixing a dimethyl silicone fluid or a polyether-siloxane copolymer with the coating material (Japanese Patent Publication No. 47-18985), a coating composition admixed with an aminoalkyl-substituted organopolysiloxane copolymer (Japanese Patent Publication No. 48-4367), a coating composition admixed with a mercaptoalkyl-substituted organopolysiloxane copolymer (Japanese Patent Publication No. 53-20530) and the like. However, the phenomenon of blocking is ineffectively prevented by the addition of dimethyl silicone fluid notwithstanding the superior performance thereof in levelling of film surfaces, prevention of the so-called "flooding" which means separation of pigment components and the like sometimes accompanied by another disadvantage of cratering or scission in the coating films due to the silicone. The use of the polyether-modified organopolysiloxane copolymer or the aminoalkyl-substituted organopolysiloxane copolymer gives no sufficient effect of anti-blocking and may induce the phenomenon of blocking by the prolonged or repeated contact of pressure-sensitive adhesive tapes although they do not cause the phenomenon of cratering or scission of the coating films. A marked effect of anti-blocking is obtained by the addition of a mercaptoalkyl-substituted organopolysiloxane copolymer but only with little effect in polyurethane-based coating materials.